Dynamics of Local Vibrational Modes in Semiconductors

技术：这个项目的目标是阐明半导体的局部振动模式(Lvms)与声子浴和电子能带结构的耦合。直接探测这些路径和速率的能力允许在新的精度水平上测试理论。嵌入在半导体中的氢特别令人感兴趣，因为相关的LVM可以被干净地激发，并且通常在能量上与声子浴很好地分开。半导体中由氢同位素组成的材料体系可能会受到这种能量途径的性质的强烈影响，因为弛豫时间可以决定半导体/氢体系的稳定性。在此之前，我们利用超快激光研究了体硅和锗中各种H、D和O相关点缺陷的振动寿命。这些研究表明，振动衰减率有100倍的异常变化。如此大的变化在固体中是不寻常的，并促使人们对此有更深的理解。这些寿命测量提供了控制硅MOSFET可靠性值的基本参数的指示。这个项目的目的是探索动力学参数的大的结构依赖性，并更好地理解局域模、声子池和电子系统之间的择优耦合。尽管与本征半导体的带隙相比，LVM的能量很小，但p型或n型半导体和激光诱导的自由载流子浓度都提供了能量可达的通道。电子通路的存在影响了种群的寿命和线宽，并可能解释了这种戏剧性的位置依赖性。这些可选的衰变通道将通过在本征材料包括Si、Ge、GaX(X=As、N、P)和ZnO中加入掺杂结构和激光诱导的e-h激发来实验研究。非技术性：该项目为包括现代光学、材料科学和计算建模在内的跨学科领域的研究生和本科生提供综合教育和研究培训。此外，了解皮秒时间尺度上的激发态寿命将描绘出物理学家、材料科学家、化学家和工程师感兴趣的晶体半导体中缺陷和杂质的振动动力学。该项目的一个重要目标是向一个更大的潜在感兴趣的调查人员社区展示这种方法的有效性。此外，这项研究在附近的托马斯·杰斐逊实验室和威廉与玛丽学院开发和支持的实验能力的组合将继续向国内和国际研究人员提供，利用这一项目的影响。

Technical: The objective of this project is to elucidate the coupling of local vibrational modes (LVMs) of semiconductors to the phonon bath, and to the electronic band structure. The ability to directly probe these pathways and rates allows tests of theory at new levels of precision. Hydrogen embedded in semiconductors is of particular interest, since the associated LVMs can be excited cleanly, and are usually well separated in energy from the phonon bath. Materials systems consisting of hydrogen isotopes in semiconductors may be strongly influenced by the nature of this energy pathway, as the relaxation time can determine the stability of the semiconductor/hydrogen system. Previously, we studied vibrational lifetimes of various H, D and O related point defects in bulk Si and Ge using ultrafast lasers. These studies indicate extraordinary variations of a factor of 100 in vibrational decay rates. Such large variations are unusual in solids and motivated a deeper understanding. These lifetime measurements give an indication of fundamental parameters controlling Si MOSFET reliability values. The aim of this project is to explore the large structural dependence of dynamical parameters, and to obtain a better understanding of preferential coupling between local modes, the phonon bath, and the electronic system. Although the energy of the LVM is small compared to the band-gap of an intrinsic semiconductor, both p- or n-type semiconductors and laser-induced free-carrier concentrations provide energetically accessible channels. The existence of electronic pathways influences population lifetimes and linewidths and may account for the dramatic site dependence. These alternative decay channels will be studied experimentally by incorporating dopant structures as well as laser-induced e-h excitation in intrinsic materials, including Si, Ge, GaX (X = As, N, P) and ZnO. Non-Technical: This project provides integrated education and research training to graduate and undergraduate students in an interdisciplinary field including modern optics, materials science and computational modeling. Additionally, understanding excited state lifetimes on a picosecond timescale will delineate vibrational dynamics of defects and impurities in crystalline semiconductors of interest to physicists, materials scientists, chemists, and engineers. An important goal of the project is to demonstrate the efficacy of this method to a much larger community of potentially interested investigators. Also, the combination of experimental capabilities developed and supported by this research at the nearby Thomas Jefferson Laboratory and at the College of William and Mary will continue to be made available to domestic and international researchers, leveraging the impact of this project.